Yaris Hybrid - low squeal sound

[unimark]

Hi all. I've had my Yaris Hybrid for just under a month now, nearly 700 miles. I've just started to notice what I can only describe as a low squeal noise when I'm driving between 5-10mph and 15-20mph. I don't think it's done this before, as a first time car owner I'm noticing every little thing almost immediately (pride and joy and all that). 

The sound will only appear when I'm accelerating through those speeds, not when I take my foot off and never appears again once I go above 20mph. It does sound like a moving noise if that makes sense, kind of like when an old car has a bad fan belt but this is much much quieter. My passenger couldn't even hear it. 

Anybody have any thoughts? 

[YarisHybrid2016]

Rather than it being a squeal, you're likely hearing the motor/generator.

If the car is stationary and you enthusiastically pull off, the combination of motor and engine start-up sounds quite futuristic IMHO. 

Another sound that is harder to hear, but you'll likely notice soon, is when you're travelling at 50-60* MPH and lift off the power and start regen braking, you can hear MG1 spin-up. The harder you regen brake, the higher pitch (higher RPM) it becomes.

* You can hear it at lower speeds, but it is more noticable at higher speeds as regen braking is more effective resulting in higher generator speeds.

[unimark]

Thanks for the reply. I'll keep an ear out (so to speak) if the noise get louder. It's almost like a rubbing sound where it would need oil. But I can't tell if it's from the wheels or engine. 

I actually tried pulling away as smooth as possible as a test and could hear the familiar hum of the electric motor but then on top of that was this new squeal sound.